A progressive cavity pump (PCP) is a device used to enable artificial lift for hydrocarbon production. A PCP has a rotor and a stator that go inside a production tubing. A motor at the top of the well turns a rod string, which turns the rotor at the bottom of the well, which makes a progressing cavity that pulls fluid in from the below the stator and pushes it out above the stator. Two problems with PCP's are that 1) they can create wear on production tubing, which necessitates pressure tests; and 2) they can cause lower joints of tubing to become loosened or disconnected.
PCP rotor rods routinely cause significant wear on the inner diameter of the production tubing string, potentially leading to tubing leaks. If the rod has eccentricity, it can rub against the inside of the production tubing and create wear spots, especially at rod joint connections.
Pressure tests are required to ensure the integrity of the production tubing prior to operation, and during the life of the well. One current method of practice is to run the tubing in hole with a bull plug, conduct a pressure test, pull the tubing out of hole, replace the bull plug with the stator, run in hole with the tubing for a second time, and then run in hole with the rotor. Every time that the tubing is re-tested, the rotor and tubing have to be pulled out of hole and the operation is repeated with this current practice.
When a progressive cavity pump is operating, there is a risk that it can cause joints of tubing to “back out.” That is, the tubing joints may become loosened or disconnected and compromise the integrity of the well.
Such a situation may occur when the stator elastomer becomes compromised due to normal well operating conditions (temperature, solubility, use, etc.). Instead of moving independently of the stator, the rotor becomes enmeshed with the stator. Due to continued torque from the motor at the wellhead, the stator begins moving with the rotor. Viewing this situation from the top of the well, down, the rotor rods, rotor, stator, and possibly a few production tubing joints above the stator all rotating clockwise. As may be appreciated, clockwise rotation of a lower joint produces the same result as counter-clockwise rotation of an upper joint, in that counter-clockwise rotation of an upper joint disconnects production tubing joints. As may be appreciated, when the production tubing joints are disconnected, well integrity is compromised, and this can lead to well failure.
While there exists certain existing technology to prevent stators and production tubing from backing out, what is needed is the ability to combine this feature with a pressure test valve.